A Ukrainian soldier stands in front of an armored personnal carrier at a checkpoint near Slovyansk on Sunday. / Kirill Kudryavtsev, AFP/Getty Images

by Peter Leonard, The Associated Press

by Peter Leonard, The Associated Press

SLOVYANSK, Ukraine - Eight European military observers held prisoner by pro-Russia forces in eastern Ukraine were marched out under armed guard on Sunday to give public assurances that they weren't being mistreated.

Germany's foreign minister condemned the appearance as "revolting" and a violation of the men's dignity. Four members of the team are German.

One of the observers, a Swedish officer, was released later in the day for medical reasons.

The insurgents in Slovyansk have taken a number of people hostage, including journalists and pro-Ukraine activists, as they strengthen their control in the east of the country in defiance of the interim government in Kiev and its Western supporters.

On Sunday, they captured three Ukrainian security service officers, who were shown to Russian journalists bloodied and blindfolded with packing tape.

Also on Sunday, a crowd of several hundred pro-Russia activists stormed the television broadcasting center in Donetsk, the regional capital of eastern Ukraine, to demand that Russian state channels be put back on the air. The Kiev government last month blocked the broadcasts of the Russian channels, which serve as propaganda tools for the Kremlin.

The crowd included several dozen men wearing camouflage fatigues and face masks, the standard uniform of the pro-Russia forces that have seized government buildings in at least 10 cities in eastern Ukraine.

Col. Axel Schneider from Germany, who spoke for the group of military observers detained Friday, emphasized that they were on a diplomatic mission under the auspices of the Organization of Security and Cooperation in Europe and weren't spying for NATO, as the insurgents claim.

Schneider said additional proof was the participation of the officer from Sweden, which is not a member of NATO.

The observers, who appeared nervous, were in the custody of armed men wearing camouflage fatigues and black balaclavas who escorted them into the Slovyansk city hall for the news conference and led them away afterward. Schneider said they were being treated as well as possible under the circumstances.

"The mayor of this city granted us his protection, and he regarded us as his guests," Schneider told journalists. "I can tell you that the word of the mayor is a word of honor. We have not been touched."

Schneider, who was speaking before the Swede was freed, said he had no information about when they would be released and that it was a matter for diplomats of their countries. The group also includes officers from Poland, Denmark and the Czech Republic.

The Swedish officer, Maj. Thomas Johansson, got into a car with OSCE representatives outside city hall and drove off with them. He was freed "on humanitarian grounds as he has a mild form of diabetes," said Stella Khorosheva, a spokeswoman for the mayor.

German Foreign Minister Frank-Walter Steinmeier condemned the display of prisoners.

"Today's public display of the OSCE observers and the Ukrainian security forces as prisoners is revolting and violates (their) dignity in a blatant fashion," he said in a statement. "This is a breach of all the rules and standards."

The German colonel said he understood that the self-proclaimed mayor, Vyacheslav Ponomarev, could use the observers as a bargaining chip.

"Our presence here in Slovyansk is for sure a political instrument for the decisionmakers here in the region and the possibility to use it for negotiations," Schneider said. "It's logical in the eyes of Mayor Ponomarev that he can use us to present his positions."

Ponomarev said Saturday that the European observers could be released in exchange for jailed pro-Russia activists.

The mayor has refused to specify how many Ukrainian journalists and activists his forces have detained, but he suggested it was several dozen.

On Sunday, the insurgents captured three Ukrainian security service officers, who were shown to journalists in the security service headquarters in Slovyansk. Stripped of their trousers and shoes, they sat with heads bowed.

Igor Strelkov, who has been identified as the commander of the armed insurgents, said the three Ukrainian officers were on a mission to seize leaders of the pro-Russia force when they were captured.

Ukraine's Security Service confirmed that its officers had been seized by armed men. The officers were on a mission to detain a Russian citizen suspected in the killing of a Ukrainian parliament member, the agency said in a statement.

The Ukrainian government and the West have accused Russia of using covert forces to encourage the unrest in eastern Ukraine, where pro-Russia militias have seized police stations and government buildings in at least 10 cities and towns.

The U.S. and other nations in the Group of Seven have announced plans to impose additional economic sanctions on Russia in response to its actions in Ukraine. The European Union also is planning more sanctions. Ambassadors from the bloc's 28 members are to meet Monday in Brussels to add to the list of Russian officials who have been hit by asset freezes and travel bans.

"The more names we add to that list, the more they do bite in the Russian economy," British Foreign Secretary William Hague said Sunday on Sky News. "But we are also working on more far-reaching measures of economic, trade and financial sanctions. â?¦ We will go ahead with them if necessary, if Russia continues to escalate this crisis."